The invention relates generally to mobile equipment, and more particularly to such equipment having a satellite reception unit and method for position finding.
The use of satellite navigation systems, for example, the global positioning system (GPS), is already known with agricultural equipment or with implements for drawing up crop registers and ground height profiles as well as monitoring fertilizer dispensing. In this case meanwhile satellite navigation systems such as differential global positioning (DGPS) are available with suitably efficient evaluation units which achieve accuracy of position finding, i.e., finding the position of a GPS antenna, to within a centimeter.
Thus, for example, from DE 196 47 523 is known an agricultural equipment with a satellite navigation system. The equipment described therein has a cultivation tool, it being proposed therein to find the position of a reference point on the cultivation tool instead of, for example, the position of the center of the equipment. There is a problem here, however, if the satellite reception unit (GPS antenna) for particular reasons cannot be mounted on the reference point of the cultivation tool. Lack of mechanical mounting facilities, shading of signals by the equipment itself, or the risk of damage or heavy wear are possible reasons for the fact that the GPS antenna cannot be mounted directly in the location whose position is actually to be found. In these cases the reference point whose position is to be found is at a distance spatially from the GPS antenna whose position is actually found by the satellite navigation system. This makes coordinate conversion necessary; i.e., from the coordinates found by satellite navigation of the GPS antenna which is, for example, located on top of the equipment, the coordinates of the reference point on the cultivation tool, which might be lower than the antenna, must be deduced by conversion. In the event that the cultivation tool is rigidly connected to the equipment, from DE 196 47 523 is obtained the instruction for finding the height coordinate of the reference point; subtract the difference in height between the mounting point of the GPS antenna and the reference point of the height-coordinate of the mounting point of the GPS antenna determined by satellite navigation for conversion. In the event that the cultivation tool is not rigidly connected to the equipment, but, for example, mounted on it with adjustable height, from DE 196 47 523 is obtained the instruction to provide a sensor which measures the change in height of the cultivation tool relative to the equipment and lets this measured change in height enter into the coordinate finding described above as a correction.
Furthermore, however, there is a general problem of position finding if the location (reference point) whose position is to be found does not coincide with the mounting point of the GPS antenna, but there is a distance between the two. And of course there is an uncertainty which stems from the fact that basically all points on the surface of a sphere with a radius of that distance, at the center of which is located the mounting point of the GPS antenna, are considered as the possible positions of the reference point. As the distance between the reference point and the GPS antenna in the case of agricultural equipment can perfectly well be several meters, the result is a correspondingly high uncertainty in position finding of the reference point, which is in itself highly unsatisfactory in view of more and more accurate navigation systems.
Of course the direction of travel and the orientation of the equipment can be determined by iteration while traveling from the position coordinates of the GPS antenna succeeding each other in time, but this method is inaccurate and fails in the case of equipment that is stationary or when starting from a standstill. Furthermore, the direction of travel does not tally with the longitudinal direction of the equipment in some applications (for example, in crab steering or on a slope).
Only if one were to make restrictions on freedom of movementxe2x80x94for instance, only travel in a N-S and/or E-W direction or only travel in the horizontal planexe2x80x94could this uncertainty be avoided. This is, however, not possible with agricultural equipment and implements hitched to them.
It is an object of the present invention to reliably allow accurate finding of a reference point which is spatially remote from the mounting point of the navigation antenna.
In accordance with the present invention there is provided a satellite antenna attached to an item of equipment and capable of receiving global positioning system transmissions, at least one sensor with the capability to determine three-dimensional distance from the satellite antenna to a reference point, and a processing unit capable of calculating the location of the reference point using the location of the satellite antenna and the distance information from the sensor.
In accordance with another aspect of the present invention is a method for position finding in the three-dimensional terrestrial reference system. The absolute position of a satellite reception unit is determined, and then at least one sensor is used to determine the distance between the satellite reception unit and a reference point spatially separated from it. Equipment-specific base conversion quantities in memory accessible to the processing unit are then used to determine with a processing unit and the data received by the satellite reception unit the absolute position of the reference point.